This invention relates to a method and apparatus for evening the sliver produced by a card, wherein conventionally a determined output rate and a determined draft is set; the actual sliver weight for a given sliver length is determined by weighing and in case of a deviation from a desired sliver weight, the draft (tension) is varied to correspond to a predetermined desired sliver thickness.
According to a known process, in case of predetermined output rate and draft, the sliver number is determined by monitoring weight measurements while sliver regulation is deactivated. By virtue of a subsequent alteration of the draft the difference between the determined (actual) sliver number and the desired sliver number may be reduced. The thus resulting change in the sliver number is verified by renewed weighing. This process is repeated as often as necessary to achieve a sufficient agreement between the desired sliver number and the measured sliver number. Subsequently, the desired sliver thickness value is determined by potentiometer balancing.
In the sliver manufacture it is an objective to produce a sliver having a determined sliver number which should remain substantially constant. According to the known process at the beginning of the manufacture a determined output rate (m/min) and a determined draft (for example, 80-fold) are set. Subsequently, a determined sliver length is sampled and weighed (first monitoring weighing) from which the actual sliver weight (g/m) and thus the actual sliver number (m/g) is obtained. In case of a deviation from the desired sliver number the draft is changed by altering the feed roller speed whereby the quantity of the fiber material supplied to the carding machine is changed. Thereafter a second monitoring weighing is performed. In case the actual sliver weight then corresponds to the desired sliver weight (that is, the actual sliver number is identical to the desired sliver number), the desired sliver thickness may be determined which is utilized as a desired value for setting a sliver regulating device. Since there is a relationship between the sliver thickness and the sliver number dependent upon the fiber material, the desired sliver thickness corresponding to the desired sliver number may be derived from such relationship. The above-described prior art method is disadvantageously complex.